1. Field of the Invention
Amitriptyline is a tricyclic antidepressant which finds extensive use. The therapeutic range for the drug is from about 50 to 175 ng/ml. Lower dosages do not have significant effect and overdosages have substantial side effects which can be life-threatening. Overdoses can be characterized by convulsions, coma, cardiac arrhythmias, and anticholinergic signs, such as mydriasis and tachycardia.
It is found that the rate of metabolism of the drug can vary widely with individuals, as well as the sensitivity of the individual to the drug. It is therefore necessary to insure proper dosage levels to monitor the plasma level, so that a therapeutic dosage level may be maintained.
In monitoring the dosage level, it is desirable that there be a simple accurate rapid technique for measuring the amitriptyline level, which can distinguish amitriptyline from other drugs and metabolites of amitriptyline, which might otherwise give an erroneous value of the amitriptyline level.
2. Brief Description of the Prior Art
Techniques reported for the determination of amitriptyline in biological fluids include the use of thin-layer chromatography, gas-liquid chromatography and GLC-mass spectrometry. Gifford, et al., J. of Chrom., 105, 107-113 (1975); Gupta, et al., Clin. Biochem., 9, 247-51 (1976); Nyberg and Martensson, J. Chromatography, 143, 491 (1977); Watson and Stewart, J. Chrom., 134, 182 (1977); ibid. 132 155-159 (1977). Radioimmunoassay has been reported for amitriptyline by Aherne, et al., Br. J. Clin. Pharmac., 3, 561 (1976), Turner, Lancet, 180, 1316 (1977); and Aherne, et al., Lancet 1214 (1977). In Aherne, et al., ibid., a synthesis for an antigen for antibody formation is described, where nortriptyline is substituted with aminobutylene followed by conjugation to bovine serum albumin employing carbodiimide. In another antigen conjugate synthesis by Kaul, et al., J. Anal. Tox., 1, 236 (1977), nortriptyline was conjugated to bovine serum albumin through a succinic group. The resulting antibodies were found to have significant cross-reactivity with a number of other tricyclic drugs.